Diameter Dependence of Magnetic Properties of Co-based Metal Fibers

Naked Co68.25Fe4.5Si12.25B15 metal fibers with diameter from 25 mu m to 100 mu m are produced by melt extraction method. Significant diameter dependence of magnetic properties is studied. Their microstructure and magnetic properties of hysteresis loops and giant magneto impedance (GMI) effect at frequencies from 0.1MHz to 13MHz are investigated. The results show that the coercivity increases with the diameter of fibers and the GMI effect is best in fiber with a diameter of 35 mu m. It is found that the cooling rate of solidification decreases with the increase of fiber diameter. And fibers are amorphous with the diameter of 50 mu m and there are nanocrystallines in fibers with a diameter of 85 mu m. The grain boundary blocks the magnetization process which makes lower circular permeability, larger coercivity and lower field sensitivity of GMI effect. The original microstructure of Co-based fibers decides their magnetic properties. Therefore, material design is important to improve the GMI effect in magnetic field sensor making.